Post by thread:[EE] single point tracking inverter for solar pane

added topic tag On Fri, Jun 8, 2012, at 12:54 PM, Justin Richards wrote: {Quote hidden}> Hi all, > > just had some solar panels installed and ended up on the East facing > roof section where is was supposed to be North facing. > > I suggested put 7 panels facing North and 1 panel facing East but they > said that it is a single tracking inverter (this inverter has two > inputs for two (collective) panels each 1500 watts. > > They said not possible as it was a single tracking inverter that it > would always default to the lowest panel or lowest denominator. I > accepted this at first, but now thinking about it, the tracking > inverter would simple pick the optimum load for maximum power > transfer. > > They also gave several other reasons why they could not put them on > the North face including > > power loss , the current is low 5amsp at 360 volts so I^2 R losses I > suspect are low over 20m. > > Any thoughts. > > justin -- http://www.fastmail.fm - Access your email from home and the web

oops, I knew something was missing in my post. thanks Bob. On 8 June 2012 13:09, Bob Blick <spam_OUTbobblickTakeThisOuTftml.net> wrote: {Quote hidden}> added topic tag > > On Fri, Jun 8, 2012, at 12:54 PM, Justin Richards wrote: >> Hi all, >> >> just had some solar panels installed and ended up on the East facing >> roof section where is was supposed to be North facing. >> >> I suggested put 7 panels facing North and 1 panel facing East but they >> said that it is a single tracking inverter (this inverter has two >> inputs for two (collective) panels each 1500 watts. >> >> They said not possible as it was a single tracking inverter that it >> would always default to the lowest panel or lowest denominator. I >> accepted this at first, but now thinking about it, the tracking >> inverter would simple pick the optimum load for maximum power >> transfer. >> >> They also gave several other reasons why they could not put them on >> the North face including >> >> power loss , the current is low 5amsp at 360 volts so I^2 R losses I >> suspect are low over 20m. >> >> Any thoughts. >> >> justin > > -- > http://www.fastmail.fm - Access your email from home and the web > >

> just had some solar panels installed and ended up on the East > facing roof section where is was supposed to be North facing East-facing will be most illuminated in the morning, and no direct illumination after that .... > I suggested put 7 panels facing North and 1 panel facing East ..... so if you wanted an early morning boost and most illumination until evening (and why not one facing West ?) I'd have thought that would be the most effective way I know MPPT inverters can be pretty smart and make the most of what's / watts available but it seems to me you're missing out on a lot of energy A quick Google - http://www.solarshop.com.au/blog/solar-myths/solar-myths-west-and-east-facing-roofs-won-t-produce-very-much-electricity but I don't see why your panels weren't installed North-facing if it was not impractical to do so, unless East-facing meets either your energy needs or is all the inverter can handle. That said though, on a miserable winter's day they might be struggling. In the summer, excess or unuseable production from North-facing panels could be shunted or burnt off with a dummy load Joe

> until evening (and why not one facing West ?) I'd have thought that > would be the most effective way > I submitted a complaint to the parent company and ended up with the installer returning. Shortly after his return a lively discussion on the roof about what was optimum followed. He finally made a honorable offer to relocate at his cost which I declined. I felt to some degree that he installed them where he thought was best and not just the easiest. I had to agree that his option included shortest cable run, easier future upgrade option. (if I do upgrade it will be on the North section) While we were on the roof, the time of day was such that the east facing panels were in shadow, at the same time as it turned out the North facing roof section was also in shadow from neighbours trees. So it seemed futile to move them. One thing we could not agree on however, was my suggestion to face some East and some North. He ended up getting some national head honcho on the phone wanting to bet $500 that the inverter would sense the worst case panel and track it. I kept stating that the tracking inverter only "sees" the array as a single power source and it will load it to achieve maximum power transfer. Both the installer and the gambler refused to accept this quoting x years installing etc and that it would track the worst panel

Justin Richards wrote: > One thing we could not agree on however, was my suggestion to face some East > and some North. He ended up getting some national head honcho on the phone > wanting to bet $500 that the inverter would sense the worst case panel and > track it. I kept stating that the tracking inverter only "sees" the array as > a single power source and it will load it to achieve maximum power transfer. > Both the installer and the gambler refused to accept this quoting x years > installing etc and that it would track the worst panel. I don't recall whether you described how your panels are wired. Keep in mind that with series-connected panels, the total voltage is the sum of the individual panel voltages, but the current through the string is limited to the current of the least-illuminated panel. This may be what the vendor was referring to. Panels (or strings of panels) wired in parallel need to have a blocking diode on each panel (or string); otherwise the better-illuminated panels will dump their current into the less well-illuminated panels. With blocking diodes, MPPT gets a bit tricky, because there may be multiple local maxima in the power vs. voltage curve of the system as the higher-voltage panels get loaded down to the point where lower-voltage panels begin conducting. It depends on how well the panels are matched, both in terms of manufacture and illumination. In the worst case, only the highest-voltage panel will be supplying all of the current. -- Dave Twee

> Keep in mind that with series-connected panels, the total voltage is the sum > of the individual panel voltages, but the current through the string is > limited to the current of the least-illuminated panel. This may be what the I had considered the current would be limited but that implies that the shaded panel's resistance is greater than zero. I accept that the panels do have a reistance, but if they are partially illuminated and generating some power them I suspect that resistance would be low. I have some panels, I should go and measure OC Voltage, CC Current and Non illuminated Resistance. Also perhaps voltage across a panel connected to perhaps a 20 ohm resistor and measure the current and voltage at various illuminations and plot. Justi

Justin Richards wrote: > > Keep in mind that with series-connected panels, the total voltage is the > > sum of the individual panel voltages, but the current through the string > > is limited to the current of the least-illuminated panel. > > I had considered the current would be limited but that implies that > the shaded panel's resistance is greater than zero. I accept that the > panels do have a reistance, but if they are partially illuminated and > generating some power them I suspect that resistance would be low. > > I have some panels, I should go and measure OC Voltage, CC Current and > Non illuminated Resistance. Also perhaps voltage across a panel > connected to perhaps a 20 ohm resistor and measure the current and > voltage at various illuminations and plot. The concept of "resistance" in a solar cell is a tricky one. A solar cell is fundamentally a diode, and this diode is pointed the "wrong way" in terms of drawing power from the cell. In other words, when functioning as a solar cell, positive current comes out of the anode, rather than going into it. The only way the cell can pass current in this direction is by means of the electron-hole pairs that are created by the incoming photons. This means that the number of electrons available to carry current -- including the current driven by other cells in series -- is directly proportional to the number of photons striking the cell. In other words, once the reverse saturation current level is reached in the cell, including the current generated by photons, the cell functions as a current source, with effectively infinite resistance. In all other regimes of operation, the V-I curve of the cell is that of a diode, where the effective resistance varies widely, depending on the current. -- Dave Twee